1. Field of the Invention
This invention is directed to systems, methods and devices for generating an electron beam.
2. Related Art
Electron beam sources are widely used in a variety of applications. Electron beam generators are used both as sources for the electron beams themselves, as charge neutralizers for charged ion beams, to produce protective thermal spacecraft coatings, to form plasma-assisted thin films, and to deposit optical coatings, such as, for example, for large mirrors, in forming metallized packaging films and in electron beam evaporation, electron beam surface modification, thin film growth, plasma-assisted chemical vapor deposition, plasma vapor deposition, electron beam curing, waste handling, and electron beam reactive deposition.
Ion beams are used both in the semiconductor manufacturing industry and many other industries, as well as in many satellites and other spacecraft, and other applications. In such satellites and other spacecraft, ion beams are used as thrusters to maneuver the satellites or other spacecraft. In the semiconductor industry, ion beams are used for a variety of purposes, including etching, ion implantation, doping, sputtering, and the like.
In both semiconductor manufacturing and spacecraft/satellite maneuvering embodiments, it is highly desirable, if not absolutely necessary, that the plasma stream, i.e., the ion beam, be electrically neutral. The ion beams are typically generated by stripping electrons off of atoms of the desired material to create positively-charged ions. These positively-charged ions are accelerated by an electric field and formed into a beam. Typically, the positively-charged ions originate in a plasma.
However, due to space-charge limitations within the ion beams, the charged ions in the ion beams tend not to stay tightly packed in the beam. Rather, the ion beam tends to “blow apart” due to the repulsive force between the similarly-charged ions. Furthermore, positively-charged ion beams are attracted to negatively-charged surfaces. For example, in the spacecraft/satellite embodiments, if the beam remains positively-charged, two problems arise. First, the spacecraft/satellite itself becomes negatively charged when the positive charge is emitted. Second, because the ion beam is positively charged, it becomes attracted to the negatively-charged spacecraft/satellite, and thus does not travel in a straight line away from the spacecraft or satellite, or, in a worst-case leave the spacecraft environment at all. Rather, the positively-charged ions move within the electric field formed by the negatively-charged spacecraft/satellite and return toward the spacecraft/satellite due to the electrostatic attraction between the negatively-charged spacecraft/satellite and the positively-charged ions. As a result, a positively-charged ion beam does not provide the proper thrust to appropriately maneuver the satellite or spacecraft.
Typically, to avoid these problems, the positively-charged ion beam is neutralized shortly after it leaves the ion beam generating device by combining the positively-charged ion beam with a beam of (negatively-charged) electrons. The combination of the electrons and positively-charged ions renders the net plasma stream neutrally charged. However, because of the relatively light weight of the electrons, relative to the ions, the electrons do not significantly affect the thrust provided by the ion beam. Moreover, by extracting equal currents of ions and electrons, no net charge accumulates in and/or on the spacecraft/satellite. Because the ions in the plasma stream are now balanced by electrons, a net electric field does not arise on the spacecraft or satellite. Thus, the plasma stream moves in a straight line away from the satellite or spacecraft, providing the desired thrust.